Poly(benxoic acid), method for the preparation thereof and method for the preparation of poly(p-phenylene) from poly(benzoic acid)

ABSTRACT

Disclosed is a novel polymeric compound poly(benzoic acid) which is a linear polymer consisting of the 1,4-phenylene linkages, each phenylene group having a carboxyl group. Poly(benzoic acid) can be prepared by hydrolyzing a poly(alkyl benzoate) in the presence of an acid or alkali. The thus obtained poly(benzoic acid) can be converted into a poly(p-phenylene) by the decarbonation reaction thereof in an organic solvent such as quinoline in the presence of metallic copper dust or a copper (II) compound such as copper (II) oxide and copper (II) carbonate hydroxide.

BACKGROUND OF THE INVENTION

The present invention relates to a poly(benzoic acid), which is a novelcompound not known in the prior art nor described in any literatures, amethod for the preparation of a poly(benzoic acid) and a method for thepreparation of a poly(p-phenylene) having electroconductivity,oxidation-reduction characteristic and excellent heat resistance andsuitable as a polymeric electroconductive material and material of aheat-resistant polymer from the poly(benzoic acid).

Poly(p-phenylene) is a known polymeric material having goodelectroconductivity and excellent heat resistance. Despite these uniqueproperties as an organic polymer, the industrial application field ofpoly(p-phenylene) is still not so wide because of the difficult problemsthat poly(p-phenylene) is an insoluble and infusible polymer so that noconventional method is applicable to the molding work of the polymer andthat the molecular weight thereof cannot be high enough with arelatively irregular molecular structure not to give a reproduciblequality.

A method for the preparation of a poly(p-phenylene) is disclosed inJournal of the American Chemical Society, volume 85, pages 454-458(1963), according to which benzene is subjected to oxidativepolymerization in the presence of aluminum chloride and copper (II)chloride. An alternative method is proposed in Synthetic Metals, volume44, pages 107-110 (1992), in which benzene is electrolyticallypolymerized in fuming sulfuric acid to give a poly(p-phenylene). Thesemethods, however, are practically defective since, in the former method,the poly(p-phenylene) is obtained in the form of a powder which is notsusceptible to molding and, in the latter method, the polymer obtainedhas only a quit low degree of polymerization with consequently poorelectric and mechanical properties although the polymer is obtained inthe form of a film deposited on the surface of the electrode.

Besides, a method is proposed in Macromolecules, volume 21, pages294-304 (1988), in which a poly(p-phenylene) is obtained in the form ofa film through an intermediate having moldability. The polymer obtainedby this method, however, does not consist of the 1,4-phenylene unitsalone but contains about 15% of the 1,2-phenylene units so that theelectric properties thereof are not as desired.

SUMMARY OF THE INVENTION

The present invention accordingly has a primary object to provide apoly(benzoic acid) which is a novel polymeric compound havingmoldability and can be an intermediate for the preparation of apoly(p-phenylene) consisting substantially of the 1,4-phenylene unitsonly as a secondary object of the invention.

Namely, the present invention provides a poly(benzoic acid) which is alinear polymer consisting of the recurring monomeric units expressed bythe chemical formula ##STR1##

In particular, a poly(benzoic acid) having a number-average degree ofpolymerization in the range from 30 to 20,000 can be readily prepared bythe method described hereinbelow.

Further, the method of the invention for the preparation of apoly(p-phenylene) comprises subjecting the above mentioned poly(benzoicacid) to a decarbonation reaction in the presence of a copper dust or acopper (II) compound.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an infrared absorption spectrum of a poly(benzoic acid)prepared in Example 1.

FIG. 2 is an infrared absorption spectrum of a poly(p-phenylene)prepared in Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The poly(benzoic acid) of the present invention, which is a novelcompound not known in the prior art, Can be prepared by the hydrolysisof a poly(alkyl benzoate) represented by the general formula ##STR2## inwhich R is a lower alkyl group having 1 to 4 carbon atoms, such asmethyl, ethyl, propyl and butyl groups, and the subscript n is apositive number giving the number-average degree of polymerization, inparticular, in the range from 30 to 2000. The hydrolysis reaction of apoly(alkyl benzoate) can be performed by using an acid or alkali as thecatalyst. The poly(alkyl benzoate), e.g., poly(methyl benzoate),poly(ethyl benzoate), poly(propyl benzoate) or poly(butyl benzoate), asthe starting material for the preparation of a poly(benzoic acid) can beprepared, for example, by the polycondensation reaction of an alkyl2,5-dichlorobenzoate, e.g., methyl 2,5-dichlorobenzoate, in the presenceof nickel bromide, triphenyl phosphine and metallic zinc according tothe procedure disclosed in Macromolecules, volume 25, page 1816 (1992).

The poly(benzoic acid) of the present invention can readily be convertedinto a poly(p-phenylene) when it is heated in an organic solvent in thepresence of a catalyst to effect decarbonation reaction. Suitablecatalysts for the decarbonation reaction include metallic copper dustand compounds of divalent copper such as copper (II) oxide, copper (II)carbonate and the like. Namely, the poly(benzoic acid) is dissolved inan organic solvent such as quinoline, N,N-dimethyl aniline and the likeand the solution, in which the above mentioned copper catalyst issuspended, is heated at a temperature in the range from 130° to 300° C.or, preferably, from 170° to 260° C. so that the poly(p-phenylene) asformed is precipitated in the solution. The thus producedpoly(p-phenylene) is insoluble in any organic solvents so that no knownmethods are applicable to the determination of the degree ofpolymerization thereof. It would be a fair assumption, however, that theabove described reactions of the hydrolysis of the poly(alkyl benzoate)and decarbonation of the poly(benzoic acid) do not affect the degree ofpolymerization of the polymer so that the average degree ofpolymerization of the thus obtained poly(p-phenylene) be identical withthat of the starting poly(alkyl benzoate).

The present invention provides a means to easily obtain a poly(benzoicacid) which is soluble in many organic solvents and capable of beingshaped into any desired forms such as a film. Accordingly, the presentinvention provides a possibility for the preparation of a shaped body,e.g., films and sheets, of a poly(p-phenylene), which is considered inthe prior art to be insusceptible to molding or shaping due to theinsolubility thereof in organic solvents, by first shaping apoly(benzoic acid) into a film or sheet followed by a decarbonationtreatment thereof in a suitable organic solvent while keeping the shapeof the Polymer as such.

In the following, examples are given to illustrate the poly(benzoicacid) and the inventive method for the preparation thereof as well asthe method for the preparation of a poly(p-phenylene) from thepoly(benzoic acid) in more detail. The Reference Example given belowpreceding the Examples describes a method for the preparation of apoly(methyl benzoate).

Reference Example

Into a three-necked flask were introduced 1.30 g of nickel (II) bromide,11.9 g of triphenyl phosphine and 12.1 g of metallic zinc dust togetherwith 90 ml of N,N-dimethyl formamide to form a reaction mixture whichwas heated at a temperature of 40° to 45 ° C. under an atmosphere ofargon with agitation. When the color of the reaction mixture turnedreddish, a solution of 12.3 g of methyl 2,5-dichlorobenzoate in 60 ml ofN,N-dimethyl formamide was added dropwise into the reaction mixturewhich was heated at 80° C. for 48 hours thereafter. After the end ofthis reaction time, the reaction mixture cooled to room temperature wasadmixed with an excess volume of acetone and agitated for 30 minutesfollowed by filtration to remove the unreacted methyl2,5-dichlorobenzoate and triphenyl phosphine. The cake of theprecipitates obtained by filtration was dispersed in an excess volume ofdiluted hydrochloric acid to dissolve the zinc dust followed byfiltration of the mixture to collect the undissolved precipitates whichwere successively washed with water, methyl alcohol and acetone followedby drying in a vacuum desiccator at 60° C. for 5 hours. The thusobtained product could be identified to be a poly(methyl benzoate)having a number-average degree of polymerization of 106. The yield ofthis product was 85% of the theoretical value.

EXAMPLE 1

A reaction mixture consisting of 5 g of the poly(methyl benzoate)prepared in Reference Example described above and 50 ml of a 20% methylalcohol solution of sodium hydroxide was heated for 1.5 hours underreflux. The reaction mixture was added to a dilute hydrochloric acid andheated therein for 10 minutes. The precipitates in the reaction mixturewere collected by filtration, washed with water and dried under reducedpressure to give a white powder which could be identified to be apoly(benzoic acid) having a number-average degree of polymerization of106. The yield of the product was approximately quantitative accordingto the stoichiometry. This poly(benzoic acid) was soluble in quinoline,pyridine and an aqueous solution of sodium hydroxide. FIG. 1 of theaccompanying drawing shows an infrared absorption spectrum of thepoly(benzoic acid). The characteristic peaks in the spectrum at wavenumbers of 1710 cm⁻¹ and 1230 cm⁻¹ could be assigned to the stretchingvibration of the C═O bond and stretching vibration of the C--O bond,respectively.

EXAMPLE 2

A reaction mixture formed by adding 3.5 g of the poly(benzoic acid)prepared in Example 1 and 0.32 g of copper (II) oxide to 50 ml ofquinoline was heated under reflux for 5 hours in an atmosphere of argon.After the end of the reaction time, the reaction mixture was admixedunder agitation with acetone to remove quinoline and the precipitatesseparated from the reaction mixture were agitated in a dilutehydrochloric acid to remove the inorganic matter. The precipitatescollected by filtration was successively washed with water and methylalcohol followed by drying in a vacuum desiccator at 60° C. for 5 hours.The thus obtained product in a powdery form could be identified to be apoly(p-phenylene) from the infrared absorption spectrum shown in FIG. 2of the accompanying drawing, in which the strong and sharp peak at about800 cm⁻¹ could be assigned to the 1,4-phenylene linkage. The yield ofthe product was approximately quantitative assuming the stoichiometry ofthe decarbonation reaction. This poly(p-phenylene) was insoluble in anyorganic solvents as well as in an aqueous alkali or acid solution.

EXAMPLE 3

A reaction mixture formed by adding 3.0 g of the poly(benzoic acid)prepared in Example 1 and 0.14 g of copper (II) carbonate hydroxide to48 ml of quinoline was heated under reflux for 5 hours in an atmosphereof argon. The reaction mixture was treated subsequently in the samemanner as in Example 2 to give a product in a powder form. This productcould be identified to be poly(p-phenylene) from the infrared absorptionspectrum which was substantially identical with that of the productobtained in Example 2. This poly(p-phenylene) product was also insolublein any organic solvents as well as in an aqueous alkali or acidsolution.

What is claimed is:
 1. A method for the preparation of apoly(p-phenylene) which comprises heating a solution of a poly(benzoicacid) in an organic solvent in the presence of metallic copper dust or acopper (II) compound as the catalyst to effect a decarbonation reaction.2. The method for the preparation of a poly(p-phenylene) as claimed inclaim 1 in which the organic solvent is quinoline or N,N-dimethylaniline.
 3. The method for the preparation of a poly(p-phenylene) asclaimed in claim 1 in which the catalyst is copper (II) oxide or copper(II) carbonate hydroxide.
 4. The method for the preparation of apoly(p-phenylene) as claimed in claim 1 in which the heating temperatureof the solution of a poly(benzoic acid) is in the range from 130° to300° C.